BGE: Expression to check if Collision Sensor's property is True or False
No Expression Required

I don't know if there's no way for a Collision Sensor to pass along the value of the property it's watching. Instead, we can have the object collided with send a Message, and receiving that Message can be one of the conditions required by an And Controller in order to trigger the Actuator.

Obstacle Logic



Cube Logic





As for expressions, here is a reference. I'll re-post it below:

Table 26-1. Valid expressions

Expression type  Example
===============  =======
Integer number   15
Float number     12.23224
Booleans         TRUE, FALSE
Strings          "I am a string!"
Properties       propname
Sensornames      sensorname (as named in the LogicBrick)


Table 26-2. Arithmetic expressions

Expression       Example
==========       =======
EXPR1 + EXPR2    Addition, 12+3, propname+21
EXPR1 - EXPR2    Subtraction, 12-3, propname-21
EXPR1 * EXPR2    Multiplication, 12*3, propname*21
EXPR1 / EXPR2    Division, 12/3, propname/21
EXPR1 &gt; EXPR2    EXPR1 greater EXPR2
EXPR1 &gt;= EXPR2   EXPR1 greater or equal EXPR2
EXPR1 &lt; EXPR2    EXPR1 less EXPR2


Table 26-3. Boolean operations

Operation        Example
=========        =======
NOT EXPR         Not EXPR
EXPR1 OR EXPR2   logical OR
EXPR1 AND EXPR2  logical AND
EXPR1 == EXPR2   EXPR1 equals EXPR2


Conditional statement: IF( Test, ValueTrue, ValueFalse )

Examples:

Table 26-4. Expression examples

Expression           Result          Explanation
==========           ======          ===========
12+12                24              Addition
property=="Carsten"  TRUE or FALSE   String comparison between a Property and a string
"Erwin"&gt;"Carsten"    TRUE            A string comparison is done


And if anyone figures out syntax for testing the value of a property, please share.